This invention relates to ionic flame monitors and more particularly to such a monitor that detects all of the characteristic components of the ionization current resulting from a flame.
Ionic flame monitoring (IFM) is a time proven method of detecting the presence of flame in fossil fuel combustion system. This particular technique for flame monitoring is primarily used for determining the existence of flame in oil and/or gas fired ignition system in industrial, utility, and commercial boilers.
The ignition system is commonly referred to as an ignitor or lighter.
One example of the use of ionic flame monitoring is described in U.S. Pat. No. 4,588,372 wherein a flame rod is used to monitor the flame in a gas burning furnace to maintain a peak flame rod current. This results in incomplete combustion due to a shortage of primary air. The furnace in that patent includes a secondary air inlet that is sized to maintain excess air in the combustion chamber for complete combustion.
During the combustion of hydrocarbon fuels, free ions and charged particles are produced making the hydrocarbon-fuel flame electrically conductive. Another combustion characteristic of a hydrocarbon-fuel flame is that it pulsates resulting in time varying numbers of free electrons and charged particles. Thus the conductivity of the hydrocarbon-fuel flame will also pulsate.
As is shown in FIG. 1 when a DC excitation voltage is applied to an electrode 10, called an IFM rod, immersed in the hydrocarbon-fuel flame 12 an ionization current 20 is produced. The ionization current 20 has as is shown in FIG. 2 a DC component 22 that is produced by a minimum number of free electrons and charged particles always being present in the flame.
The ionization current also has an AC component 24 that is the result of the changes in conductivity produced by the flame pulsation, and a flicker frequency 26, also known as the pulsation frequency, arising from the pulsation of the flame. The DC intensity 22, AC intensity 24, and flicker frequency 26 of the ionization current 20 changes with the stability and quality of the hydrocarbon-fuel flame.
Existing ionic flame monitoring electronic packages typically measure one or more of these three characteristic components to determine if the fuel on an ignition system is burning. If flame is present a flame relay is energized and if there is no flame the relay is de-energized. The flame relay contact(s) are typically input into some form of combustion safety control system.
Ignition systems are problematic pieces of equipment subject to a number of operational problems. Historically ionic flame monitoring equipment only provides a flame relay contact output indicting flame does or does not exist. Typically, the electronic hardware cannot be adjusted and does not provide any feedback to the operators about the quality of the flame or operational condition of the firing equipment. Thus, existing ionic flame monitoring electronics are simply flame switches and nothing more.
It is a well established fact in the combustion industry that there is a relationship between the quality of flame and the ionization current in an ionic flame monitoring system. As the mixture of fuel and air comes closer to stoichometric conditions, the number of ions and free electrons increases thereby making the flame more conductive. For years boiler service engineers have used voltmeters to monitor the power supply voltage on an IFM rod and use the drop in voltage as an indicator that a good flame exists. Ionic flame monitoring is even used in analytical instruments to measure gas quality and fuel/air ratio.
The ionic flame monitor of the present invention measures all three ionization current parameters and presents these values in real time to operating and service personnel. The information is presented to the operator through a digital display as well as through a digital output port. The measurement of all three parameters and the presenting of information in real time to operators about those parameters allows the operator to track changes in the three parameters and thereby obtain an early warning that a problem is developing in the ignitor. Further the direction of the changes can be an indicator of a specific problem. Existing ionic flame monitors only use one or two of these parameters and may not display them in real time.
An ionic flame monitor. The flame monitor has a flame rod that produces an ionization current when the flame rod is immersed in a flame and excited by a voltage. The ionization current has a DC component and an AC component each dependent on the intensity of the flame, and a flicker frequency.
The flame monitor also has a computing device that has at least first, second and third inputs. The flame monitor further has a first circuit connected to the first input of the computing device, the first circuit responsive to the ionization current for producing at the first input an AC signal representative of the flicker frequency; a second circuit connected to the second input of the computing device, the second circuit responsive to the ionization current for producing at the second input a signal having an amplitude proportional to the ionization current AC component; and a third circuit connected to the third input of the computing device, the third circuit responsive to the ionization current for producing at the third input a signal which is related to the ionization current DC component. The computing device is responsive to the signals at the first, second and third computing device inputs for determining the existence of the flame.